The present invention relates to a converter device, a rotating electrical machine control device and a drive device.
Japanese Patent Application Publication No. JP-A-2003-324942 describes converter control for a bidirectional converter for performing a step-up operation for efficiently power-driving an electric motor and a step-down operation for charging a battery with regenerative electric power of the electric motor. In this converter control, the temperature of the bidirectional converter is detected, and a PWM controlled carrier frequency for switching on and off a step-up switching transistor is lowered in order to reduce heat generation and thus to prevent thermal destruction of the transistor. At this time, the carrier frequency is gradually lowered in order to prevent noise generated by a reactor in the converter from being suddenly changed in tone (noise, strange feeling, and abnormal noise) by the change in carrier frequency.
Japanese Patent Application Publication No. JP-A-2004-135465 also describes converter control for a bidirectional converter. In this converter control, the reactor temperature of the bidirectional converter is detected, and a carrier frequency that reduces noise corresponding to the temperature is extracted by map matching. The extracted carrier frequency is determined to be a PWM controlled carrier frequency for switching on and off a step-up switching transistor.
Japanese Patent Application Publication No. JP-A-2006-324942 describes torque control of an on-vehicle electric motor. In this torque control, the reactor temperature of a bidirectional converter and the coolant temperature are detected. When a difference between the detected temperatures is small (poor cooling capability), a torque command value (target torque) is limited to suppress a temperature increase. In order to suppress a sudden torque change (shock) caused by limiting the torque command value, an annealing process is performed to correct a step change of temperature detection data to a gently inclined change.
A wide rotation speed range and a wide torque range are required for a wheel driving motor. Therefore, in order to precisely control the output torque and the motor speed by PWM control, it is difficult to control the carrier frequency and the ON-duty width of PWM pulses in the whole operation range if a power supply voltage is constant. Moreover, the amount of harmonic components in an applied voltage of the motor increases as the ON-duty width is reduced. As a result, a motor loss (core loss) is increased, causing increase in power loss. In order to solve this problem, a motor control device for boosting a battery (primary side power supply) voltage using a boost converter to control the applied voltage of the motor to a wide range extending above from the battery voltage. Thus, the operation region of the wheel driving motor can be extended, for example, from the “operation region at battery voltage” to the “operation region during step-up operation”. During braking operation of a vehicle, the wheel driving motor is controlled to a regeneration mode, and a bidirectional converter additionally having a step-up function to step down regenerative electric power of the motor to charge a battery is used, whereby vehicle driving is economically improved. Each of Japanese Patent Application Publications JP-A-2003-324942, JP-A-2004-135465, and JP-A-2006-324942 discloses a vehicle drive device using a bidirectional converter.
In both of a boost converter and a bidirectional converter, the conditions that are thermally the harshest for a reactor are during step-up operation and when a motor output is high. Factors that cause heat generation in the reactor under these conditions are a ripple current that flows through the reactor in response to turning on and off a step-up switching element and a direct current that is output from a battery through the reactor to a motor via the step-up switching element or a diode. In order to prevent heating of the reactor, a device that limits a target torque of the motor or limits the direct current has been used in related art. A target torque is limited in Japanese Patent Application Publication No. JP-A-2006-324942.